This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Anticancer drugs induce tumor drug-resistance and metastasis, and cancer stem cells display more resistant than other differentied cancer cells;however, little is known whether anticancer drugs promote cancer stem cells. The goal of this project is to determine the role of ceramide glycosylation in mediating cancer stem cells during the course of chemotherapy. To complet the goal, we pursued two specific aims in last year: 1), determine the increasements of glucosylceramide synthase (GCS) and breast cancer stem cell (BCSC) in drug-resistant cancer cells;2), identify the induction of doxorubicin in cancer stem cells via ceramide glycosylation in vivo. We found that GCS overexpression was interrelated to the increment BCSCs and drug-resistance in human breast cancer MCF-7 cell lines after doxorubicin induction. With GCS overexpression, the BCSCs of CD24-/CD44+/ESA+ phenotype was increased by 5-fold in MCF-7/Dox cells as compared to MCF-7 cells. Silencing GCS by using mixed-backbone oligonucleotide (MBO-asGCS) significantly decreased the numbers of BCSCs more than 2-fold. BCSCs sorted displayed 3-fold higher GCS enzyme activity and formed 2-fold more colonies, as compare with other non-stem cell subsets. The BCSCs cells showed significantly higher tumorigenicity and metastasibility as compared to non-stem cells in athymic nude mice. More interestingly, doxorubicin treatment considerably increased BCSCs by 2-fold in tumors, and MBO-asGCS treatment eliminated the tumor growth and reduced metastasis due to reduction of BCSCs. Comparison of glycosphingolipids and gene profile indicated GCS or globo-series glycosphingolipids regulates FGF1 and others to accumulate BCSCs. These results demonstrate that ceramide glycosylation accumulates BCSCs formation and causes aggressive tumor progression.